System for fixing the heating resistance in a cooker plate

ABSTRACT

The system for the attachment of a heating element in a electric cooking hob comprises a flat electrical element made of a thin resistance alloy strip, a horizontal porous insulating base ( 4 ) supporting the heating element ( 2 ) and a plurality of feet ( 3 ) for attachment to the base ( 4 ), which are inserted in said base ( 4 ) and hold vertical the element ( 2 ) in place. The heating element ( 2 ) is same width (w) throughout its length, and stands on the surface of the insulating base ( 4 ) without the need for a housing groove, and the fixing are flat feet ( 3 ) each one bent along their central vertical zone ( 3   c ) coinciding with the element ( 2 ) bending, to facilitate the secure attachment of the element ( 2 ).

The present invention relates to an electrical heating elementstructurally coupled to an insulating support base and especiallyadapted for a cooking hob.

PRIOR ART

Electrical cooking hobs are known whose heating element is made from afine flat alloy strip, the element first being wound and then attachedsupported at the edge on the horizontal insulating base of the hob. Themeans of attachment used are either lugs or feet forming part of theelement, emerging from one edge at regular intervals along the length,or removable clamps fitted over the element. The tips of the feet orclamps are inserted in the porous insulating base to attach the element.The attachment feet create an uneven conductive section along theelement causing differences of temperature which increase the effect offatigue due to cyclic heat stresses, particularly in non-ductile alloyssuch as chrome or nickel.

EP-612199 describes an electrical element of the above sort. To limitthe mean conductive section of the element and make it more even, thestrip is pressed with cuts in the feet in the form o openings or groovesto remove material. This also reduces heat dissipation toward theattachment feet. Heating element solutions with integral feet require achange of matrix to die-cut the element, when a different spacing isrequired between feet.

U.S. Pat. No. 4,161,648 (DE-2551137) describes another design for a flatelement with attachment feet inserted in the insulating base.

The conductive length of the heating element is increased in relation toits overall length by cutting slits alternately from each edge of theflat strip, to form a zig-zag conductor of smaller conductivecross-section than the width of the strip. The strip slitting reducesthe rigidity of the element in all directions and particularlyvertically. The rigidity of the heating element and the tendency to bendhave the adverse effect of warping the insulating base.

ES-2079293 (P9302122) describes a system for attaching the flat elementto the insulating base. The element does not have attachment feet andits lower edge fits into a vertical groove in the base in spiral form.The element is attached to the base after fitting, by inserting invertedU-shaped attachment clamps spaced evenly on the element, which press itagainst the bottom of the housing groove. Because there are no integralattachment feet, the full width and material of the original strip areemployed as the element's conductive section. The drawback of this knownsolution is the insertion of the clamps, after the element has beenfitted on the groove in the insulating base, which is laborious andsusceptible of errors which cause partial shearing of the conductivesection and undesired local curving.

DISCLOSURE OF THE INVENTION

The object of the invention is a flat electrical heating element fittedto a porous insulating base of a cooking hob heater, as defined in claim1.

The invention provides the combined advantages of the disclosed priorart designs. In the absence of integral attachment feet, the heatingelement according to the invention can be employed as an elementthroughout the entire width of the strip, the conductive section of theelement is even throughout its length, heat stresses caused by uneventemperatures are reduce, at the same time as having the advantage of theconsistency of bending offered, by attachment clamps together with thesecure attachment of the element to the base. A further advantage overthe examples cited in the Prior Art is, the variety of intervals of thelength of the strip or spacing between two attachment points, foradaptation to any cooking hob. Moreover, the spacing between feetconditions the element's placement upon the insulating base throughoutthe cooking hob's life.

The attachment feet are preferably an inverted U-shape and their flatwalls remain in contact with the element around the bending line sothat, in relation to the mass of the feet, a moment of force ispermitted for insertion which is greater that admitted by integral feetin the Prior Art solution, so that the housing groove in the insulatingbase can be done away with.

The feet are made of an alloy similar to those of the element, so thatheat expansion in terms of volume does not have effects of deformation,displacement or transversal curving different from that of the element.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevation view of the heating element according to thedesign in the invention, before forming.

FIG. 2 is a perspective view of the element in FIG. 1 before attachment.

FIG. 3 is an elevation view of the element in FIG. 2 arranged on theinsulating base of a cooking hob.

FIG. 4 is a view of a clamping foot for attaching the element as inFIGS. 1-3.

DETAILED DESCRIPTION OF THE INVENTION

An embodiment of the heating element 1 according to the invention isshown in FIG. 3. In an initial operation, as shown in FIG. 1, theinverted U-shaped feet 3 have been fitted on the element 2; in a secondoperation, as shown in FIG. 2, the element is bent into a zig-zag form,with the bend coinciding with the central zone 3 c of the feet 3, benttogether, and finally the bent element 2 is attached to the insulatingbase 4 of the cooking hob by inserting the tips 3 a of the feet under avertical force F until edge 2 a of the element 2 comes into contact withthe surface of the insulating base 4, thus without the need of a housinggroove in the insulating base 4.

The heating element 2 is made of thin, flat alloy strip of, for example,thickness e close to 0.05 mm and width w between 3 and 9 mm, making ithighly sensitive to mechanical stresses applied during fitting. Theplacement of the feet 3 at constant intervals “p” along the length ofthe element 2, allows automatic fitting devices to be used for theirpre-programmed positioning, followed by precise bending along thecentral line 3 c. The feet 3, as shown in FIG. 4, are preferably aninverted U-shape, and their side walls 3 b remain in contact with theelement 2 around the bending zone 3 c. Other shapes of cross-section ofthe feet 3, not shown in the drawings, are permitted for the embodimentof the invention, e.g. an inverted V-shape to facilitate its previousfitting on the element 2, or an inverted U-shape to limit the mass ofthe feet.

I claim:
 1. A system for the attachment of a heating element in aelectric cooking hob, comprising: a radiant heater provided with aninsulating base, which is made of a porous material and placedhorizontal, supporting the heating element, said electric heatingelement constructed from a elongated thin strip of a continuous width,and made of a electrical resistance alloy, a plurality of fixing meansfor attaching the electric heating element to the insulating base, whichare distributed along the heating element at a determined constantinterval of length, and inserted in the insulating base keeping verticalthe heating element in place on its strip edge on the base surface,wherein the fixing means are in form of flat feet previously fitted onto the heating element, and bent along a central vertical zonecoinciding with the heating element bending and superimposed to it,having each foot at least one wall on one of the heating element faces,to facilitate the its secure attachment of the element in relation tothe insulating base surface, being the heating element placed verticalwithout the need for a housing groove on the base surface.